Considered to be one of the most impressive examples of medieval Bulgarian architecture, the Round Church takes its name from the distinctive shape of one of its three sections, the cella (naos), which is a rotunda that serves as a place of liturgy.

The church's design also includes a wide atrium and a rectangular entrance area, or narthex, marked by two circular turrets.

The church has been likened to examples of religious architecture from the late Roman (Early Christian) period, the Caucasus, and the Carolingian Pre-Romanesque of Charlemagne because of its characteristic plan, which is significantly different from contemporaneous Bulgarian or Byzantine buildings.

Medieval inscriptions on the walls range from names of saints in Byzantine Greek to separate letters and short texts in the Glagolitic and Cyrillic alphabets.

[3] The Round Church was constructed during the rule of Boris' son and successor, Simeon (r. 893–927), whose successful campaigns established Bulgaria's temporary superiority over Byzantium,[4] at times threatening the Byzantine capital at Constantinople.

[7] Intended more as a royal residence and a showcase of cultural power than a fortress, the city boasted impressive architecture,[5] including a large number of characteristic palaces and dozens of churches.

[15][19] While the church can be ascribed to no later than the 10th century, some scholars have suggested that it may have been constructed directly on top of a much earlier late Roman basilica due to its antiquated plan.

[24] Another researcher, Krastyu Miyatev, sees it as a royal church of Simeon,[25] but art historian Nikola Mavrodinov and archaeologist Totyu Totev insist it belonged to a monastery from the beginning.

[26][27] The earliest excavations of the site were carried out in 1927–1928 by archaeologists from the National Archaeological Museum in Sofia and the Bulgarian Antiquities Society under the direction of Yordan Gospodinov.

[28] In 1927, the Round Church, along with the entirety of medieval Preslav, was proclaimed a historical and archaeological reserve and placed under state protection as a national antiquity.

In 1970, it was individually included in the list of monuments of culture of national importance with a publication in that year's State Gazette, issue 46.

[25] It is most likely based on the abundant examples of late Roman or early Byzantine buildings that lay ruined in the Bulgarian lands.

Another possible model for the Round Church in Preslav may well be found in Carolingian architecture from the time of Charlemagne, and particularly the Palatine Chapel in Aachen, western Germany, with which it shares some characteristics.

[46] One trait of the Round Church that is claimed by scholars to be a very recognisable Carolingian influence is the presence of a monumental westwork.

[48][49] The Round Church includes three sections: the wide atrium (or courtyard), the narthex and the cella (also naos or, due to its shape, rotunda), each serving as a premise to the other.

[50] Mavrodinov and archaeologist Karel Škorpil believe the narthex and cella comprised the first building period, while the atrium was added very shortly after that and by the same architect.

[26] Together with the north and south wall, the entrance of the narthex effectively isolates two smaller parts of the atrium, similar in plan[16] and accessible through doors.

However, Nikolova considers its shape much too unusual and its depth unsuitable for baptism, and believes it may instead have been designed as a vessel for dispensing holy water.

A circle of ten[55] or twelve[26][43][53] white marble[53] columns was inscribed inside the rotunda, 0.55 m (1.8 ft) from the interior buttresses.

The marble ambon was situated in the center of the circle of columns and of the whole rotunda, directly under the dome's centre,[16][38][56] as evidenced by a mortar padding.

[53][58] With the exception of the Corinthian and Doric column capitals, which are of Roman or Byzantine origin, the rest of the decoration was created specifically for and during the church's construction.

[59] Mavrodinov goes a step further to claim that the architect of the Round Church was directly inspired by ancient examples, citing in particular the rich sculptural decoration.

[62] Tiles found inside the church ruins depict birds and other animals in addition to geometric shapes and floral motifs, all glazed in either brown, yellow, green, blue, or blue-green.

[20] The Glagolitic inscriptions of the Round Church bear evidence that the use of that alphabet in Preslav continued alongside Cyrillic.

The inscription was clumsily written on top of a mortar putty and says in translation: "Church of Saint John, built by chartophylax Paul".

Nikolova considers it more likely that the author of the inscription was a literate person who served under chartophylax Paul and desired to spread his fame.

[65] Individual letters inscribed on the walls illustrate the way Greek and simplified Glagolitic letterforms were combined to form the early Cyrillic alphabet.